This invention relates generally to radiation detection apparatus and more particularly to radiation detection apparatus adapted to detect radiation at two different wavelengths.
As is known in the art, radiation detectors are used in a wide range of applications. In one application, an array of the infrared detectors is used to detect the infrared energy emitted by objects in a scene under observation. Each infrared detector generates an electrical charge in response to the portion of the emitted energy it detects. Electrical read out circuitry is provided for converting the generated charge into a corresponding electrical signal. The electrical signals are combined by a processor which produces a corresponding visual image of the observed scene. Thus, each detector provides the data for a corresponding pixel of the produced visual image.
In one arrangement, the infrared detectors are formed as an array of electrically isolated photo-diode detectors along one surface of a semiconductor chip, typically a chip of InSb or HgCdTe. Each photo-diode in the array generates an electrical current representative of the amount of infrared power focused to it. The current is integrated by an integration circuit, typically a capacitor to produce an electrical signal representative of the infrared energy impinging the photo-diode detector. The integrated signal is read out and passed to the processor. In one arrangement, the read out circuit is formed as an integrated circuit in a second semiconductor chip, typically Si. More particularly, an array of read out circuits is arranged in a matrix of rows and columns formed in the second semiconductor chip. Each one of the read out circuits is disposed in vertical alignment, or registration with, and is electrically connected to, a corresponding one of the photo-diode detectors. Thus, the first and second semiconductor chips are disposed in overlaying parallel planes. This arrangement allows for the direct electrical connection between each photo-diode detector and its associated read out circuit.
While such arrangement provides suitable detection at one wavelength of the emitted infrared energy, in some applications it is desirable to simultaneously detect energy in two different wavelengths for each pixel.